PHP is the software that delivers web pages to the world. When you type a URL into web browser's address bar, you are sending a message to the web server at that URL. Asking it to send you an HTML file. The web server responds by sending the requested file. Hypertext Preprocessor. PHP code can be inserted into the HTML of a Web page. When a PHP page is accessed, the PHP code is read or parsed by the server the page resides on.